For producing a crushed product by crushing a food raw material, such as a biological material, organic material, chemical substance or so on, there have practically been used a technique in which a pair of opposingly disposed crushing discs, such as a stone mill, is used for crushing the food raw material. In this technique, the raw material to be crushed, such as a food raw material, is supplied between a pair of opposingly disposed crushing discs, wherein the raw material is crushed in between the two crushing discs by rotating at least one of the crushing discs to produce a crushed product.
On the crusher face of the stone mill are formed grooves running radially from a central portion thereof. The raw material to be crushed is supplied to the mill gap between the two crushing discs via a feed entrance port disposed in the central portion at a location biased from the center, in which the raw material is at first only roughly crushed in the central region of the mill gap and is expelled aside succeedingly to the outer region where it is subjected to fine crushing. Conventional crushing techniques using a stone mill or the like suffers, however, from an inconvenience, that a cereal raw material having a thin flexible skin layer, such as wheat, buckwheat or soybean, can be crushed only insufficiently, in which the substance of albumen can be crushed finely, but the substance around the flexible skin layer cannot be crushed finely and the roughly crushed grains of larger particle sizes will pass through the mill gap and are collected at the disc periphery.
In such a crushing technique, therefore, it is not able to obtain a fine powdery crushed product of a uniform particle size as a whole. In an attempt to increase the productivity by a size reduction of the apparatus in such conventional techniques, it may be considered to use steel crushing discs to realize a high speed rotation, however, it is difficult to effect fine crushing of the material around the thin flexible skin layer. Also, in other measures using a roller mill and other types of crushers, there may be encountered a similar inconvenience.
When an apparatus of the crushing disc rotation type is operated at a high speed rotation, the resulting crushed product is apt to suffer from a debasement in quality, such as taste, mouth feel and the like, due to superfluous heat and oxidation, causing a denaturation of the component substances in the raw material. Apparatuses of the crushing disc rotation type may, in general, be constructed with a mechanism in which one of the crushing discs is rotated by a driving means and the driving mechanism is complicated due to a biased driving, so that there is some difficulty in cooling the driving side elements. Thus, cooling of the driving side crushing disc may be achieved only difficultly, though the stationary side crushing disc may be cooled easily. Therefore, it is difficult to prevent quality debasement of the resulting crushed product in such an apparatus.
As a countermeasure for improving such a problem, there has been proposed in Patent Document 1 (JPA 2005-87816), a process and an apparatus for producing a crushed product by establishing a crushing section between confronting crusher faces of a pair of crushing discs, in which a rotatable crushing disc is rotated by means of a driving device wherein a stationary crushing disc is cooled by a cooling part and the raw material is supplied to the crushing section to effect the crushing thereof while supplying a cooled inert gas to the crushing section to replace atmospheric oxygen gas included in the raw material by the inert gas and, at the same time, to cool the raw material, whereupon the resulting crushed product is guided out from the crushing section into a crushed product receiver. Here, it is proposed that the spent inert gas which has been used for cooling the raw material is guided to the rear face of the rotatable crushing disc to cool the rotatable crushing disc. However, it suffers from a problem that the cooling of the rotatable crushing disc may be difficult to attain, since the rotatable crushing disc is subjected to heating due to heat transfer from the driving device connected thereto.
In Patent Document 2 (JPA 11-151080), there is disclosed a method of freeze-drying, in which the material to be treated is mixed with dry ice and is crushed to thereby cause the material to be frozen to subject it to freeze-drying, while replacing the gas phase with the thereby generated carbon dioxide gas. However, it is not disclosed therein that a raw material is crushed by means of a pair of crushing discs to produce crushed product while preventing debasement of the product quality.